Method and apparatus for a combined fuel cell and hydrogen purification system

ABSTRACT

Fuel cell systems and associated methods of operation are provided whereby application of a fuel cell is coordinated with a fuel processor and a hydrogen separator. One such method includes the following steps: (1) operating a fuel processor to convert a hydrocarbon to reformate; (2) reacting the reformate in a fuel cell to generate electrical power; (3) supplying the electrical power to an electrical load, wherein the electrical load has a power requirement threshold; (4) determining whether the electrical power from the fuel cell is below the power requirement threshold; (5) increasing a flow of reformate from the fuel processor to the fuel cell when the electrical power from the fuel cell is below the power requirement threshold; (6) flowing a portion of the reformate from the fuel processor to a hydrogen separator; (7) storing hydrogen from the hydrogen separator in a hydrogen storage vessel; (8) monitoring an amount of hydrogen stored in the hydrogen storage vessel; and (9) adjusting a proportional valve upstream from the fuel cell toward a closed position when the amount of hydrogen in the hydrogen storage tank is below a predetermined threshold to increase a proportion of the reformate from the fuel processor that is flowed to the hydrogen separator.

This application is a continuation of U.S. patent application Ser. No.10/251,133, entitled “METHOD AND APPARATUS FOR A COMBINED FUEL CELL ANDHYDROGEN PURIFICATION SYSTEM,” filed on Sep. 20, 2002.

BACKGROUND

The invention generally relates to a method and apparatus for a combinedfuel cell and hydrogen purification system.

A fuel cell is an electrochemical device that converts chemical energyproduced by a reaction directly into electrical energy. For example, onetype of fuel cell includes a polymer electrolyte membrane (PEM), oftencalled a proton exchange membrane, that permits only protons to passbetween an anode and a cathode of the fuel cell. At the anode, diatomichydrogen (a fuel) is reacted to produce protons that pass through thePEM. The electrons produced by this reaction travel through circuitrythat is external to the fuel cell to form an electrical current. At thecathode, oxygen is reduced and reacts with the protons to form water.The anodic and cathodic reactions are described by the followingequations:H_(2→2)H⁺+2e⁻  (1)at the anode of the cell, andO₂+4H⁺+4e⁻→2H₂O  (2)at the cathode of the cell.

A typical fuel cell has a terminal voltage of up to about one volt DC.

For purposes of producing much larger voltages, multiple fuel cells maybe assembled together to form an arrangement called a fuel cell stack,an arrangement in which the fuel cells are electrically coupled togetherin series to form a larger DC voltage (a voltage near 100 volts DC, forexample) and to provide more power.

The fuel cell stack may include flow field plates (graphite composite ormetal plates, as examples) that are stacked one on top of the other. Theplates may include various surface flow field channels and orifices to,as examples, route the reactants and products through the fuel cellstack. The flow field plates are generally molded, stamped or machinedfrom materials including carbon composites, plastics and metal alloys. APEM is sandwiched between each anode and cathode flow field plate.Electrically conductive gas diffusion layers (GDLs) may be located oneach side of each PEM to act as a gas diffusion media and in some casesto provide a support for the fuel cell catalysts. In this manner,reactant gases from each side of the PEM may pass along the flow fieldchannels and diffuse through the GDLs to reach the PEM. The GDL'sgenerally comprise either a paper or cloth based on carbon fibers. ThePEM and its adjacent pair of catalyst layers are often referred to as amembrane electrode assembly (MEA). An MEA sandwiched by adjacent GDLlayers is often referred to as a membrane electrode unit (MEU), or alsoas an MEA. Common membrane materials include Nafion™, Gore Select™,sulphonated fluorocarbon polymers, and other materials such aspolybenzimidazole (PBI) and polyether ether ketone. Various suitablecatalyst formulations are also known in the art, and are generallyplatinum-based.

A fuel cell system may include a fuel processor that converts ahydrocarbon (natural gas or propane, as examples) into a fuel flow forthe fuel cell stack. For a given output power of the fuel cell stack,the fuel flow to the stack must satisfy the appropriate stoichiometricratios governed by the equations listed above. Thus, a controller of thefuel cell system may monitor the output power of the stack and based onthe monitored output power, estimate the fuel flow to satisfy theappropriate stoichiometric ratios. In this manner, the controllerregulates the fuel processor to produce this flow, and in response tothe controller detecting a change in the output power, the controllerestimates a new rate of fuel flow and controls the fuel processoraccordingly.

The fuel cell system may provide power to a load, such as a load that isformed from residential appliances and electrical devices that may beselectively turned on and off to vary the power that is demanded by theload.

Thus, the load may not be constant, but rather the power that isconsumed by the load may vary over time and abruptly change in steps.For example, if the fuel cell system provides power to a house,different appliances/electrical devices of the house may be turned onand off at different times to cause the load to vary in a stepwisefashion over time. Fuel cell systems adapted to accommodate variableloads are sometimes referred to as “load following” systems.

Fuel cell systems generally include various sources of heat, such asfrom fuel processing systems, the fuel cell stack itself, exhaust gasoxidizers, etc. In particular, the exhaust from a fuel cell is generallyoxidized to remove trace amounts of unreacted fuels before it isexhausted to ambient. Such exhaust is generally hot and saturated withwater vapor from the fuel cell system and from combustion of combustiblegas components in the exhaust. For a variety of reasons, it may bedesirable to recover such heat from a fuel cell system. As examples ofsuch systems in the prior art, the teachings of U.S. patent Ser. Nos.09/728,227 and 09/727,921 are hereby incorporated by reference.

Hydrogen purification systems have also been used with fuel cell systemsin various ways. For example, a hydrogen purification system can be usedto filter a reformate stream to produce a pure hydrogen stream that canbe stored or used by a fuel cell. Hydrogen purification systems havealso been used to recover hydrogen from fuel cell system exhauststreams. In the context of this invention, a hydrogen purificationsystem may also be referred to as a hydrogen separator, and in eithercase, such a system can refer to any of the various techniques known inthe art for separating hydrogen from gas streams, includingelectrochemical separation and pressure swing adsorption systems. Asexamples of such systems in the prior art, the teachings of U.S. Pat.No. 6,280,865, Ser. Nos. 10/214,022, 10/213,798, and 10/214,019 arehereby incorporated by reference.

There is a continuing need for fuel cell system designs and improvementsto coordinate the integrated operation of systems including theforegoing.

SUMMARY

The invention provides fuel cell systems and associated methods ofoperation whereby application of a fuel cell is coordinated with a fuelprocessor and a hydrogen separator.

In one aspect, the invention provides a fuel cell system that includes afuel processor, a fuel cell, a hydrogen separator, and an oxidizer. Thefuel processor is coupled to the fuel cell via a first flow path, and tothe hydrogen separator via a second flow path. The exhaust of the fuelcell is coupled to the oxidizer via a third flow path. The second flowpath is coupled to the oxidizer via a fourth flow path. The second flowpath includes a first valve adapted to regulate flow from the fuelprocessor to the hydrogen separator. The fourth flow path includes apressure regulator, such that reformate from the fuel processor to thesecond flow path is flowed to the fourth flow path through the pressureregulator to the oxidizer when the first valve is closed.

The term “coupled” is used to refer to any direct or indirect connectionbetween two elements of the system. As an example, an indirectconnection of two components may include connections to various othercomponents between them. Also, in the context of the present invention,the term “flow path” generally refers to any conduit or housing throughwhich the flow of a process stream is guided in the system. In somecases, different flow paths can be partially coextensive, as in the casewhere a common conduit splits into two conduits.

An advantage of such systems is that in some cases, the pressureregulator and first valve can be configured such that the oxidizerreceives a slip stream of reformate to maintain the fuel celltemperature when only the hydrogen separator is in use.

For illustration purposes, the discussion provided herein focuses on PEMfuel cell systems. For example, systems under the invention may utilizea PEM fuel cell having an operating temperature less than 100° C. Also,the fuel cell may form a portion of a fuel cell stack. It will beappreciated that the invention may also be used with other types of fuelcells, such as solid oxide, phosphoric acid, molten carbonate, etc.

Various valve configurations may be used as the “first valve” referencedabove. For example, the first valve can be a proportional valve (a valvethat can be opened to a variable extent) or a modulated binary valve (avalve that is either fully open or fully closed). A modulated binaryvalve can achieve the same effect as a proportional valve byperiodically opening and closing. Valves used with the present inventionare preferably automatically controlled, but the invention is notintended to be limited by a specific valve design.

Suitable pressure regulators under the present invention includeorifices, spring-biased valve assemblies, and other types of pressureregulators known in the art. In some cases, a pressure regulator canhave a set flow restricting character, as in the case of an orifice, andin other cases, an adjustable pressure regulator can be used.

In embodiments utilizing an electrochemical hydrogen separator, theelectrical current used by the hydrogen separator can be supplied by thefuel cell, by a battery, or by some other source, such as a power grid.In some cases, a combined fuel cell and electrochemical hydrogenseparation stack can be used, as described in U.S. Pat. No. 6,280,865,Ser. Nos. 10/214,022, 10/213,798, and 10/214,019.

In another aspect, a fuel cell system is provided that includes a fuelprocessor, a fuel cell, an electrochemical hydrogen separator, and anoxidizer. The fuel processor is coupled to the fuel cell via a firstconduit. The first conduit is coupled to a second conduit via a firstjunction, such as a “Y” or “T” fitting. The first conduit includes afirst valve between the first junction and the fuel cell. The secondconduit is coupled to a first electrode of the electrochemical hydrogenseparator, i.e., the electrode from which hydrogen is separated from thereformate. The second conduit includes a second valve between the firstjunction and the electrochemical hydrogen separator. The waste streamsof the fuel cell and the electrochemical hydrogen separator are eachcoupled to the oxidizer. An outlet of the electrochemical hydrogenseparator (e.g., the purified hydrogen stream) is coupled to a hydrogenstorage vessel. The hydrogen storage vessel includes a hydrogen tap,which can be a valve assembly to provide access to the hydrogen storagetank by an external application. For example, the hydrogen storagevessel can be used as a refueling station for hydrogen powered vehiclesor other devices. In some cases, a compressor is located between theelectrochemical hydrogen separator and the hydrogen storage vessel andadapted to pressurize the hydrogen storage vessel with hydrogen from theelectrochemical hydrogen separator. In other cases, the storage vesselis pressurized by the hydrogen separator itself.

In another aspect, the invention provides a fuel cell system including afuel processor, a fuel cell, an electrochemical hydrogen separator andan oxidizer. The fuel processor is coupled to the fuel cell via a firstconduit. The first conduit is coupled to a second conduit via a firstjunction. The first conduit includes a proportional valve between thefirst junction and the fuel cell. The second conduit is coupled to afirst electrode of the electrochemical hydrogen separator. The secondconduit includes a binary valve between the first junction and theelectrochemical hydrogen separator. The waste streams of the fuel celland the electrochemical hydrogen separator are each coupled to theoxidizer.

A controller is coupled to each of the proportional and binary valves.The controller is adapted to close the binary valve when theelectrochemical separator is in an off mode, and to open the binaryvalve when the electrochemical hydrogen separator is in an on mode. Thecontroller is also adapted to adjust the proportional valve toward aclosed position in the on mode to increase a portion of reformate flowedto the electrochemical hydrogen separator. For example, as theproportional valve is closed, a backpressure will form upstream from theproportional valve and the reformate will increasingly tend to flowthrough the second conduit.

In another aspect, the invention provides a fuel cell system including afuel processor, a fuel cell, an electrochemical hydrogen separator, ahydrogen storage vessel, and an oxidizer. The fuel processor is coupledto the fuel cell via a first conduit. The first conduit is coupled to asecond conduit via a first junction. The first conduit includes aproportional valve between the first junction and the fuel cell. Thesecond conduit is coupled to a first electrode of the electrochemicalhydrogen separator. The second conduit includes a binary valve betweenthe first junction and the electrochemical hydrogen separator. The wastestreams of the fuel cell and the electrochemical hydrogen separator areeach coupled to the oxidizer.

A controller is coupled to the proportional valve, the binary valves,the fuel cell, and the hydrogen storage vessel. The controller isadapted to close the binary valve when the electrochemical separator isin an off mode, and to open the binary valve when the electrochemicalhydrogen separator is in an on mode. In the on mode, the controller isalso adapted to adjust the proportional valve toward a closed positionto increase a flow of reformate to the electrochemical hydrogenseparator according to a hydrogen demand signal from the hydrogenstorage vessel, and to increase a flow of reformate from the fuelprocessor according to a hydrogen demand signal from the fuel cell. Asan example, the hydrogen demand signal from the separator can be anindication that a pressure storage vessel associated with the separatoris running low on hydrogen. As another example, the hydrogen demand fromthe fuel cell can be a signal indicating that the output of the fuelcell needs to be increased to meet an electrical load on the fuel cell(e.g., a current and load measurement, or a voltage measurement of thefuel cell, or other load-following techniques known in the art).

In another aspect, the invention provides a method of coordinatingoperating of a fuel cell with a fuel processor and a hydrogen separationsystem, including at least the following steps: (1) operating a fuelprocessor to convert a hydrocarbon to reformate; (2) reacting thereformate in a fuel cell to generate electrical power; (3) supplying theelectrical power to an electrical load, wherein the electrical load hasa power requirement threshold; (4) determining whether the electricalpower from the fuel cell is below the power requirement threshold; (5)increasing a flow of reformate from the fuel processor to the fuel cellwhen the electrical power from the fuel cell is below the powerrequirement threshold; (6) flowing a portion of the reformate from thefuel processor to a hydrogen separator; (7) storing hydrogen from thehydrogen separator in a hydrogen storage vessel; (8) monitoring anamount of hydrogen stored in the hydrogen storage vessel; and (9)adjusting a proportional valve upstream from the fuel cell toward aclosed position when the amount of hydrogen in the hydrogen storage tankis below a predetermined threshold to increase a proportion of thereformate from the fuel processor that is flowed to the hydrogenseparator.

In some embodiments, the step of determining whether the electricalpower from the fuel cell is below the power requirement thresholdincludes determining whether a voltage of the fuel cell is below apredetermined threshold.

In some embodiments, the step of storing hydrogen from the hydrogenseparator includes operating a compressor to compress the hydrogen.

In some embodiments, the step of monitoring an amount of hydrogenstorage in the hydrogen storage vessel includes monitoring a pressure ofthe hydrogen storage vessel.

Embodiments of such methods can also include any of the features, designaspects, techniques and methods described herein, either alone or incombination. Advantages and other features of the invention will becomeapparent from the following description, drawing and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an integrated fuel cell system under an embodiment of thepresent invention.

FIG. 2 is an integrated fuel cell system under an embodiment of thepresent invention.

FIG. 3 is an integrated fuel cell system under an embodiment of thepresent invention.

DETAILED DESCRIPTION

Referring to FIG. 1, an integrated fuel cell system 100 is shown underan embodiment of the present invention. A fuel processor 102 receivesnatural gas (or some other hydrocarbon feed) 104 and air 106 andproduces a reformate stream that is output through conduit 108. As anexample, a suitable fuel processor design is described in U.S. patentSer. No. 10/184,291, which is hereby incorporated by reference. Othersuitable fuel processor designs are also known in the art.

Conduit 108 is coupled to a first junction 110, from which the reformatestream is divided into conduits 112 and 114. Conduit 112 feeds reformateto fuel cell stack 116, where hydrogen from the reformate is reacted toproduce electricity that is supplied to a load (not shown). In thisexample, the fuel cell stack 116 is comprised of PEM fuel cells, and hasan operating temperature of about 65° C., and a reactant inlet pressureof about 0.5 psig (and a reactant exhaust pressure at ambient pressure).For simplicity, the oxidant supply system associated with the fuel cellstack 116 is not shown.

Spent reformate is exhausted from the fuel cell stack 116 via conduit118 to oxidizer 120, where it is reacted with oxygen. The oxidant supplysystem associated with the oxidizer 120 is also not shown. In thisexample, the oxidizer 120 is a ceramic monolith that has beenwash-coated with a platinum catalyst. The oxidizer 120 has an operatingtemperature of about 800° C. Excess air is supplied to the oxidizer inorder to lower the oxidizer temperature as necessary. Heat from theoxidation of hydrogen and other residual combustibles in the oxidizer120 is recovered with a coolant circuit (not shown) to make steam tohumidify the reactants flowed to the fuel cell, and to maintain the fuelcell operating temperature. The exhaust from the oxidizer is vented toambient.

In some embodiments, a bypass line (not shown) is placed from conduit108 directly to the oxidizer 120. For example, conduit 108 may include athree-way valve (not shown) that can be used to bypass reformate flowdirectly to the oxidizer 120 on start-up when the reformate may betemporarily off-specification or when heat may be needed to warm up thesystem.

Conduit 114 is coupled to a second junction 122 that divides thereformate flow into conduits 124 and 126. Conduit 126 includes valve130, and feeds reformate to hydrogen separator 132. Valve 130 can be anumber of valve configurations. For example, the valve can be aproportional valve (a valve that can be opened to a variable extent) ora modulated binary valve (a valve that is either fully open or fullyclosed).

In this example, the hydrogen separator 132 is an electrochemicalhydrogen separator. The hydrogen separator 132 receives power from fuelcell stack 116 (connection not shown). Pure hydrogen is exhausted fromhydrogen separator 132 via conduit 134 to hydrogen storage vessel 136.The hydrogen storage vessel 136 can be a pressure tank, or other systemsfor storing hydrogen that are known in the art, such as metal hydridesystems. In this example, the hydrogen separator 132 is used topressurize the storage vessel 136 with hydrogen. In some cases, it maybe desirable to include a valve (not shown) along the conduit 134 toprevent back diffusion of hydrogen from the storage vessel 136 throughthe hydrogen separator 132 when the separator 132 is not in use (e.g.,is in an off mode). It may also be desirable in some cases to include acompressor (not shown) along conduit 134 to pressurize the storagevessel 136 with the purified hydrogen stream from the separator 132.

One application for the present invention is as a stationary power plantproviding a refueling means for hydrogen powered vehicles. Thus, storagevessel 136 may include a tap, valve, quick connect mechanism, or someother means of transferring hydrogen from the vessel 136 to an externalapplication. In other embodiments, it may also be desirable to plumb thesystem such that hydrogen from the vessel 136 can be supplied to thefuel cell stack 116 when desired (e.g., to meet a transient loadincrease on the stack 116).

Conduit 124 includes a pressure regulator 128, and feeds reformate tooxidizer 120. Suitable pressure regulators under the present inventioninclude orifices, spring-biased valve assemblies, and other types ofpressure regulators known in the art. In some cases, a pressureregulator can have a set flow restricting character, as in the case ofan orifice, and in other cases, an adjustable pressure regulator can beused.

Controller 138 is coupled to fuel cell stack 116, fuel processor 102,and valve 130. As an example, the controller 138 may monitor the fuelcell stack 116 to determine when a cell voltage in the stack 116 fallsbelow a predetermined threshold (e.g., 0.4 volts) to indicate when thereactant flows to the fuel cell stack 116 need to be increased (e.g.,when the load on the stack 116 is increased). The controller 138 thensignals the fuel processor system 102 (e.g., the reactant blowersfeeding the fuel processor) to increase the flow of reformate intoconduit 108.

Some embodiments may include a three-way valve (not shown) at thejunction 110, such that all of the reformate from fuel processor 102 isfed either to stack 116, or to hydrogen separator 132. In otherembodiments, a proportional three-way valve, or an equivalent pair ofvalves can be actuated and dynamically adjusted to selectively divide asupply of reformate between the fuel cell stack 116 and the hydrogenseparator 132.

As an example, where the hydrogen separator 132 is in use (e.g., in anon mode), but the fuel cell stack 116 is not in use, there maynevertheless be a need to maintain the fuel cell stack 116 at itsoperating temperature to keep it ready for future use. Valve 130 (e.g. aproportional valve) can be closed enough that a backpressure formsupstream from the valve 130 that is great enough to cause a desiredamount of reformate to flow through pressure regulator 128 to theoxidizer 120 to produce a desired amount of heat (e.g., as indicated bya temperature associated with the stack 116).

In some embodiments, the controller 138 may also be coupled to thehydrogen separator 132 or the hydrogen storage vessel 136 to coordinatethe output of fuel processor 102 with the actuation of valve 130. Forexample, a pressure sensor (not shown) on the storage vessel 136 can beused to indicate a need for hydrogen production by the hydrogenseparator 132. The output of the fuel processor 102 to conduit 114 canthus be increased and the position of valve 130 can be adjusted towardan open position until the desired amount of reformate flow to theoxidizer 120 (or heat generated by the oxidizer) is achieved. Thisprocess can be repeated until there is no longer a hydrogen demandsignal associated with the hydrogen separator 132. In an alternateembodiment, the pressure regulator 128 can be another proportional valvethat is coupled to the controller 138, which can adjust the valve 128 asneeded to achieve the foregoing objectives.

Referring to FIG. 2, an integrated fuel cell system 200 is shown underan embodiment of the present invention. A fuel processor 202 receivesnatural gas 204 and air 206 and produces a reformate stream that isoutput through conduit 208. Conduit 208 is coupled to a first junction210, from which the reformate stream is divided into conduits 212 and214. Conduit 212 feeds reformate to fuel cell stack 216, where hydrogenin the reformate is reacted to produce electricity that is supplied to aload. For simplicity, the oxidant supply system associated with the fuelcell stack 216 is not shown.

Spent reformate is exhausted from the fuel cell stack 216 via conduit218 to oxidizer 220, where it is reacted with oxygen. The oxidant supplysystem associated with the oxidizer 220 is also not shown. In someembodiments, a bypass line (not shown) is placed from conduit 208directly to the oxidizer 220. For example, conduit 208 may include athree-way valve (not shown) that can be used to bypass reformate flowdirectly to the oxidizer 220 on start-up when the reformate may betemporarily off-specification and when heat may be needed to warm up thesystem.

Conduit 214 is coupled to hydrogen separator 232. In this example, thehydrogen separator 232 is an electrochemical hydrogen separator. Thehydrogen separator 232 receives power from fuel cell stack 216(connection not shown). Pure hydrogen is exhausted from hydrogenseparator 232 via conduit 234 to hydrogen storage vessel 236. The wastestream from the hydrogen separator 232, which may contain residualhydrogen, is flowed to the oxidizer 220 via conduit 221.

The hydrogen storage vessel 236 can be a pressure tank, or other meansfor storing hydrogen known in the art, such as metal hydride systems. Inthis example, the hydrogen separator 232 is used to pressurize thestorage vessel 236 with hydrogen. As previously discussed, the storagevessel 236 may include a tap 238 as a means of transferring hydrogenfrom the vessel 236 to an external application.

Conduits 208 and 212 may be referred to collectively as a first conduit.Conduit 214 may be referred to as a second conduit. Conduit 214 iscoupled to a first electrode of the electrochemical hydrogen separator232 (e.g., the electrode from which hydrogen is separated). A valve 240between the junction 210 and the hydrogen separator 232 regulates theflow to the separator 232. Likewise, a valve 242 between the junction210 and the fuel cell stack 216 regulates the flow of fuel to fuel cellstack 216.

While valves 240 and 242 can be virtually any type of valve, in apreferred embodiment, valve 240 is a binary valve and valve 242 is aproportional valve. The control of the system 200 is thus simplifiedsince dynamic control is needed only for valve 242. The flow resistancethrough valve 240 and conduit 214 is configured to be greater than thatassociated with flow through conduit 212 and valve 242. Thus, when valve242 is fully open, reformate will preferentially flow through fuel cellstack 216. To increase the flow of reformate to the hydrogen separator232, valve 242 can be adjusted toward a closed position. As valve 242 isclosed, if the fuel cell 216 needs more reactant flow to respond to anelectrical load, then the output of the fuel processor 202 can beincreased.

Alternatively, valve 240 can be a proportional valve and valve 242 canbe a binary valve. As an example, when hydrogen is needed in the storagevessel 236, valve 240 is opened in steps. At each step, the output ofthe fuel processor 202 is increased if there is not sufficient fuelbeing fed to the fuel cell stack 216 to supply the load on the stack216. In this manner, the system continues to open valve 240 and readjustthe output of the fuel processor 202 until hydrogen is no longer neededin the hydrogen storage vessel 236.

In some embodiments, it may be preferable to operate the fuel processor202 at constant output (e.g., the fuel processor 202 may have a numberof output settings that may be selected), such that the either the fuelcell 216 or the hydrogen separator 232 is given priority, and theportion of the reformate flow that is not utilized is processed by theother device.

In some embodiments, it may be preferable to operate the hydrogenseparator 232 at steady state. For example, when hydrogen is needed inthe storage vessel 236, the separator 232 is cycled on at a set outputand then is turned off when hydrogen is no longer needed. Alternatively,the hydrogen separator 232 may also be operated in a variable outputmode that may be coordinated with the demands of the fuel cell stack 216for reactants and the remaining output capacity of the fuel processor202. Systems may also include manual overrides of such configurations sothat an operator can select a priority for how the reformate isprocessed (e.g., power to the building is shut down while the hydrogenstorage tank 236 is charged).

Referring to FIG. 3, an integrated fuel cell system 300 is shown underan embodiment of the present invention. A fuel processor 302 receivesnatural gas 304 and air 306 and produces a reformate stream that isoutput through conduit 208. Conduit 308 includes 3-way valve 341 thatcan be used to bypass reformate flow directly to the oxidizer 320 viabypass conduit 309 (e.g., while the system warms up during a cold startsequence). Conduit 308 also includes valve 342, which regulatesreformate flow to the fuel cell stack 316. Direct current from the fuelcell stack 316 is conditioned by power conditioner 348 and supplied toelectrical load 339. For example, load 339 can be a power grid within abuilding, and the load can vary depending on the appliances in use inthe building. In such cases, power conditioner 348 inverts the powerfrom the fuel cell stack 316 to alternating current with a voltagesuitable for use in the building (e.g., 120 volts). The load 339 canalso be a direct current load, such as for powering a motor or charginga bank of batteries, etc.

Spent reformate is exhausted from the fuel cell stack 316 via conduit318 to oxidizer 320, where it is reacted with oxygen. In this example,the hydrogen separator 332 is an electrochemical hydrogen separator. Thehydrogen separator 332 receives power from fuel cell stack 316(connection not shown). Pure hydrogen is exhausted from hydrogenseparator 332 via conduit 334 to hydrogen storage vessel 336. The wastestream from the hydrogen separator 332, which may contain residualhydrogen, is flowed to the oxidizer 320 via conduit 318. It may bedesirable to include check valves to each conduit flowing exhaust intoconduit 318 to prevent backflow into the system. In other embodiments,it may be desirable to plumb each exhaust stream directly to theoxidizer 320.

The hydrogen storage vessel 336 can be a pressure tank, or other meansfor storing hydrogen, such as metal hydride systems. In this example,the hydrogen separator 332 is used to pressurize the storage vessel 336with hydrogen. As previously discussed, the storage vessel 336 mayinclude a tap 338 as a means of transferring hydrogen from the vessel336 to an external application, such as a vehicle refueling station.

Between valves 341 and 342, conduit 308 is coupled to a first junction310, from which the reformate stream can be diverted to conduit 314,through valve 340, and to hydrogen separator 332. Conduit 314 is coupledto a first electrode of the electrochemical hydrogen separator 332(e.g., the electrode from which hydrogen is separated). A valve 340between the junction 310 and the hydrogen separator 332 regulates theflow to the separator 332. Likewise, a valve 342 between the junction310 and the fuel cell stack 316 regulates the flow of fuel to fuel cellstack 316.

While valves 340 and 342 can be virtually any type of valve, in apreferred embodiment, valve 340 is a binary valve and valve 342 is aproportional valve. The control of the system 300 is thus simplifiedsince dynamic control is needed only for valve 342. The flow resistancethrough valve 340 and conduit 314 is configured to be greater than thatassociated with flow through conduit 312 and valve 342 (e.g., throughthe selection of valves with desired flow resistances, through plumbingsized or configured for flow resistance, or through the use of pressureregulators). Thus, when valve 342 is fully open, reformate willpreferentially flow through fuel cell stack 316. To increase the flow ofreformate to the hydrogen separator 332, valve 342 can be adjustedtoward a closed position. As valve 342 is closed, if the fuel cell needsmore reactant flow to respond to an electrical load, then the output ofthe fuel processor 302 can be increased.

Alternatively, valve 340 can be a proportional valve and valve 342 canbe a binary valve. As an example, when hydrogen is needed in the storagevessel 336, valve 340 is opened in steps. At each step, the output ofthe fuel processor 302 is increased if there is not sufficient fuelbeing fed to the fuel cell stack 316 to supply the load on the stack316. In this manner, the system continues to open valve 340 and readjustthe output of the fuel processor 302 until hydrogen is no longer neededin the hydrogen storage vessel 336.

Controller 338 is shown coupled to the fuel processor 302, the fuel cellstack 316, valve 342, valve 340 and pressure sensor 337, and can beprogrammed or configured as know in the art to achieve the logicaloperations described above.

Still referring to FIG. 3, but in different terms, the invention canalso be illustrated as a method of operating such systems. For example,such a method might include the following steps: (1) operating a fuelprocessor 302 to convert a hydrocarbon to reformate; (2) reacting thereformate in a fuel cell 316 to generate electrical power; (3) supplyingthe electrical power to an electrical load 339, wherein the electricalload 339 has a power requirement threshold (e.g., a magnitude associatedwith the load); (4) determining whether the electrical power from thefuel cell 316 is below the power requirement threshold (e.g., whethersufficient power is being output from the fuel cell stack 316); (5)increasing a flow of reformate from the fuel processor 302 to the fuelcell 316 when the electrical power from the fuel cell 316 is below thepower requirement threshold; (6) flowing a portion of the reformate fromthe fuel processor 302 to a hydrogen separator 332; (7) storing hydrogenfrom the hydrogen separator 332 in a hydrogen storage vessel 336; (8)monitoring an amount of hydrogen (e.g., a pressure or mass of hydrogen)stored in the hydrogen storage vessel 336; and (9) adjusting aproportional valve (e.g., valve 342) upstream from the fuel cell 316toward a closed position when the amount of hydrogen in the hydrogenstorage tank 336 is below a predetermined threshold to increase aproportion of the reformate from the fuel processor 302 that is flowedto the hydrogen separator 332.

Embodiments of such methods can also include any of the features, designaspects, techniques and methods described herein, either alone or incombination.

While the invention has been disclosed with respect to a limited numberof embodiments, those skilled in the art, having the benefit of thisdisclosure will appreciate numerous modifications and variationstherefrom. It is intended that the invention covers all suchmodifications and variations as fall within the true spirit and scope ofthe invention.

1. A fuel cell system comprising: a fuel processor to provide areformate flow; a fuel cell to receive at least part of the reformateflow; an oxidizer; a hydrogen separator; and a control system toallocate part of the reformate flow to the hydrogen separator andanother part of the reformate flow to the oxidizer.
 2. The fuel cellsystem of claim 1, wherein the control system comprises a valve tocontrol communication of the reformate flow with the hydrogen separator.3. The fuel cell system of claim 1, wherein the control system comprisesa pressure regulator to control communication of the reformate flow withthe oxidizer.
 4. The fuel cell system of claim 1, wherein the oxidizeris adapted to receive exhaust flow from the fuel cell.
 5. The fuel cellsystem of claim 1, further comprising a hydrogen storage tank connectedto the hydrogen separator to store hydrogen produced by the hydrogenseparator.
 6. A method, comprising: providing a reformate flow from afuel processor; using at least part of the reformate flow to produce anelectrochemical reaction inside a fuel cell; separating at least part ofthe reformate flow into hydrogen; and automatically allocating a part ofthe reformate flow that is used for the separation and another part ofthe reformate flow that is not subject to the separation.
 7. The methodof claim 6, wherein the automatically allocating comprises using a valveto control the reformate flow to a hydrogen separator.
 8. The method ofclaim 6, further comprising: storing the hydrogen in a hydrogen storagetank.
 9. The method of claim 8, wherein the automatically allocating isbased on an amount of hydrogen stored in the hydrogen storage tank. 10.The method of claim 6, further comprising: routing said other part ofthe reformate flow to an oxidizer.